1. Field of the Invention
The present invention relates to an image tracking device which is preferably utilized in a system handling a moving situation of a vehicle in its running direction, such as an automatic tracking system, an environment recognition system and the like.
2. Discussion of Background
A device which employs an image sensor has conventionally been well known as an image tracking device. FIG. 11 is a block diagram showing an example of an image tracking device. In FIG. 11, a numeral 1 designates a lens and 3, an image sensor which is disposed apart from the lens 1 by a focal length of f, wherein an optical system (image tracking means) is constructed by the lens 1 and the image sensor 3. A numeral 6 designates an A/D converter, 8 and 8', memories, 10, a CPU, 12, a window forming device and 13, a window setting switch.
In this image tracking device, an image of an object 5 is formed on the image sensor 3 by the lens 1. An image signal provided by the image sensor 3 is converted into a digital signal by the A/D converter 6, and is stored in the memories 8 and 8'. At this occasion, the image signal is alternately stored to the memories 8 and 8'. The image signals stored in the memories 8 and 8' are electrically superposed by successively shifting them, with respect to a tracking window which is previously set for the object 5 through the window setting switch 13. A new tracking window is set with respect to an image which agrees the most with a preceding image.
In this way, the tracking window is automatically renewed, that is, the tracking window is automatically moved thereby performing the tracking of the object 5. A detailed explanation has been given to a method of achieving the tracking function in Japanese Unexamined Patent Publication No. 195916/1991, and therefore, the explanation thereof will be omitted in this specification.
It is possible to apply this image tracking device to an automatic tracking system, wherein a tracked vehicle is determined and is automatically tracked. In this case, it is necessary to constantly monitor in the running direction, and to provide safety against an unexpected appearance of a vehicle other than the tracked vehicle due to its cutting-in, change of lane and the like. For instance, in case wherein a cut-in vehicle comes into view, the safety is provided by releasing the automatic tracking upon the detection of the cut-in vehicle, or the like.
However, in the above automatic tracking system, when the monitoring in the running direction is performed by employing an obstacle sensor such as a laser radar, it is difficult to differentiate the vehicle from the background, and therefore, the monitoring in the running direction can not be performed with certainty.